This invention relates generally to cardiac rhythm management systems, and particularly, but not by way of limitation, to a cardiac rhythm management system, that provides staggered non-overlapping pulses for coordination therapy.
When functioning properly, the human heart maintains its own intrinsic rhythm, and is capable of pumping adequate blood throughout the body""s circulatory system. However, some people have irregular cardiac rhythms, referred to as cardiac arrhythmias. Such arrhythmias result in diminished blood circulation. One mode of treating cardiac arrhythmias uses drug therapy. Drugs are often effective at restoring normal heart rhythms. However, drug therapy is not always effective for treating arrhythmias of certain patients. For such patients, an alternative mode of treatment is needed. One such alternative mode of treatment includes the use of cardiac rhythm management system. Such a system may be implanted in a patient to deliver therapy to their heart.
Cardiac rhythm management systems include, among other things, pacemakers. Pacemakers deliver timed sequences of low energy electrical stimuli, called pace pulses, to the heart, such as via a transvenous lead wire or catheter (referred to as a xe2x80x9cleadxe2x80x9d) having one or more electrodes disposed in or about the heart. Heart contractions are initiated in response to such pace pulses (this is referred to as xe2x80x9ccapturingxe2x80x9d the pacing heart). By properly timing the delivery of pace pulses, the heart can be induced to contract in proper rhythm, greatly improving its efficiency as a pump. Pacemakers are often used to treat patient""s hearts exhibiting bradyarrhythmias, that is, hearts that beat too slowly.
Cardiac rhythm management systems also include cardioverters or defibrillators that are capable of delivering higher energy electrical stimuli to the heart. Defibrillators may be used to treat patient""s hearts exhibiting tachyarrhythmias, that is, hearts that beat too fast. Such too-fast heart rhythms also cause diminished blood circulation because the heart isn""t allowed sufficient time to fill with blood before contracting to expel the blood, resulting in the heart pumping a reduced amount of blood. Such pumping by the heart is inefficient. A defibrillator is capable of delivering a high energy electrical stimulus. The high energy electrical stimulus interrupts the tachyarrhythmia, allowing the heart to reestablish a normal rhythm for the efficient pumping of blood. In addition to pacemakers, cardiac rhythm management systems also include, among other things, pacer/defibrillators that combine the functions of pacemakers and defibrillators, drug delivery devices, and any other systems or devices for diagnosing or treating cardiac arrhythmias.
Cardiac rhythm management systems are also used in the treatment of congestive heart failure. Congestive heart failure can occur when the left and right ventricles do not contract simultaneously, but rather, they contract one ventricle after the other ventricle. This reduces the pumping efficiency of the heart. Moreover, in the case of left bundle branch block, for example, different regions within the left ventricle may not contract together in a coordinated fashion. Generally congestive heart failure can be treated by biventricular coordination therapy that provides pacing pulses to both right and left ventricles. See. e.g., Mower, U.S. Pat. No. 4,928,688. Normally, intrinsic signals originate in the sinoatrial node in the upper right atrium, traveling through and depolarizing the atrial heart tissue such that resulting contractions of the right and left atria are triggered. The intrinsic atrial heart signals are received by the atrioventricular node which, in turn, triggers a subsequent ventricular intrinsic heart signal that travels through and depolarizes the ventricular heart tissue such that resulting contractions of the right and left ventricles are triggered substantially simultaneously.
One problem faced by cardiac rhythm management systems in treating congestive heart failure is that, coordination therapy may require issuing stimulation pace pulses simultaneously in more than one region of a heart to ensure these regions contract in a coordinated manner. For example, coordination therapy may require applying pacing stimulation to one or both ventricles or multiple sites within one or more ventricles in a pattern that coordinates the ventricular contraction sequence. Such therapy is believed to improve systolic function of patients with ventricular conduction disorders. During simultaneous pacing of multiple regions of the heart, the resulting electric fields generated between the pacing sites may interact. This may result in unwanted and unexpected currents between the pacing electrodes at different sites such as different chambers of the heart and can affect the ability of the pacing pulses to capture the heart at the simultaneous pacing sites. Such interactions can become greater when the coordination pacing pulses have different voltage amplitudes due to the resulting electric fields between the pacing sites. Another problem with issuing biventricular coordination pace pulses simultaneously in more than one chamber is that these interactions can result in very inefficient pacing methods, one example being that it may transform cathodal pacing pulse into anodal pacing pulse.
These interactions can increase when a bipolar right ventricular electrode configuration is used with a single left ventricular electrode. In this configuration, one of the right ventricular electrodes provides a common return path, for the right and left ventricular stimulations. During such interactions, the simultaneous biventricular capture cannot be assured if left ventricular and right ventricular capture is tested separately.
When the pace pulses are delivered to a heart, leftover charge (recharge pulses) from pacing regions is discharged from the heart. These recharge pulses may also interact with pace pulses or other recharge pulses at different heart locations. This too may result in unwanted interactions between different sites.
Generally simultaneous pacing of multiple regions of a heart can be advantageous in the treatment of congestive heart failure, however; such simultaneous pacing at different pacing sites may result in unwanted interactions between different pacing sites. These interactions may result in undesirable results, such as loss of capture at the pacing sites. Thus, there is a need to eliminate unwanted interactions between electrodes at different pacing sites of a heart.
The above mentioned shortcomings, disadvantages and problems are addressed by the present subject matter, which will be understood by reading and studying the following specification. The present subject matter provides, among other things, a cardiac rhythm management system that eliminates interactions between electrodes at multiple pacing sites of a heart. This is accomplished by providing an offset between adjacent pacing and/or recharge pulses to electrodes in various regions of a heart to eliminate the interactions at different pacing sites. This improves the treatment for congestive heart failure by providing the required/programmed level of energy to the pacing sites. The present system provides an offset between pulses to eliminate the interactions during unichamber, bichamber, or multisite pacing with or without intersite stimulation delays to restore proper coordination between different chambers and between different intra chamber regions of the heart.
According to one aspect of the present subject matter, a pulse delivery controller receives pulses from a pulse generator and then delivers the pulses to multiple electrodes located at different pacing sites in a desired sequence to avoid any interactions between electric fields surrounding the electrodes during pulsing at different pacing sites. After delivering the pacing pulses, discharging of the recharge pulses begins from the respective pacing sites. During discharging, the pulse delivery controller further offsets recharge pulses to eliminate interactions between recharge and pacing pulses. Similar pulse sequencing takes place every subsequent cardiac cycle interval.
In one embodiment of providing coordination therapy, the system issues a time delay between the left and right ventricular pacing and recharge pulses to avoid any interactions between the leads. In another embodiment, the system issues a time delay between pulses (pace and/or recharge) associated with the right atrial, and right ventricular leads, and a time delay between pulses associated with right and left ventricular pulses to avoid any interactions between these leads. In another embodiment the system issues a time delay between pulses associated with left cardiac chamber electrode and the right cardiac chamber electrode to avoid any interactions between these leads. In another embodiment the system issues a time delay between pulses associated with right cardiac chamber electrode and the left cardiac chamber electrode to avoid any interactions between these leads.
Other aspects of the present subject matter will be apparent on reading the following detailed description of the invention and viewing the drawings that form a part thereof.